Phagotrophic Protists Modulate Copper Resistance of the Bacterial Community in Soil

Protist predation is a crucial biotic driver modulating
bacterial
populations and functional traits. Previous studies using pure cultures
have demonstrated that bacteria with copper (Cu) resistance exhibited
fitness advantages over Cu-sensitive bacteria under the pressure of
protist predation. However, the impact of diverse natural communities
of protist grazers on bacterial Cu resistance in natural environments
remains unknown. Here, we characterized the communities of phagotrophic
protists in long-term Cu-contaminated soils and deciphered their potential
ecological impacts on bacterial Cu resistance. Long-term field Cu
pollution increased the relative abundances of most of the phagotrophic
lineages in Cercozoa and Amoebozoa but reduced the relative abundance
of Ciliophora. After accounting for soil properties and Cu pollution,
phagotrophs were consistently identified as the most important predictor
of the Cu-resistant (CuR) bacterial community. Phagotrophs
positively contributed to the abundance of a Cu resistance gene (copA) through influencing the cumulative relative abundance
of Cu-resistant and -sensitive ecological clusters. Microcosm experiments
further confirmed the promotion effect of protist predation on bacterial
Cu resistance. Our results indicate that the selection by protist
predation can have a strong impact on the CuR bacterial
community, which broadens our understanding of the ecological function
of soil phagotrophic protists.

原生生物捕食作为一种调节细菌种群和功能特征的生态学关键生物驱动因素，其作用至关重要。先前基于纯培养的研究表明，在原生生物捕食的压力下，具有铜（Cu）抗性的细菌相较于铜敏感细菌展现出显著的适应性优势。然而，不同原生生物食草者自然群落对自然环境中细菌铜抗性的影响尚不明确。本研究中，我们对长期铜污染土壤中的摄食性原生生物群落进行了特征描述，并解析了其潜在生态学影响对细菌铜抗性的作用。长期田间铜污染显著提升了多数摄食性谱系在Cercozoa和Amoebozoa中的相对丰度，但降低了Ciliophora的相对丰度。在考虑土壤特性和铜污染因素后，摄食性生物被一致确认为预测铜抗性（CuR）细菌群落最重要的指标。摄食性生物通过影响铜抗性（copA）基因的累积相对丰度，正向贡献于铜抗性生态集群的丰度。微宇宙实验进一步证实了原生生物捕食对细菌铜抗性的促进作用。我们的研究结果指出，原生生物捕食的选择作用对铜抗性细菌群落具有显著影响，从而拓展了我们对土壤摄食性原生生物生态功能的理解。